It came from the USGS ftp site. It starts out as a set of ascii files and several fortran programs which merge the 4 ascii files into one direct access file plus an index file and a number to name file.

I translated the fortran to TrueBasic to run on a PC. I also wrote a program to display all or part of it as a graphic image, not a true map projection but just "fit the data to the screen" so I could see what it was doing.

If you're interested in doing this and think it's worthwhile, you can download it or I can send you what I have.

Roger